The invention relates to a method for determining the charging of a charcoal filter with gases or vapors and also relates to an apparatus for applying this method. Charcoal filters are used for removing gases and vapor from air. Therewith the ability of charcoal and in particular of impregnated charcoal is used to bind gases and vapors by physical and chemical absorption. When the filer is charged or loaded with gases and vapors the filtering capacity of the filter is reduced until the filter becomes inactive when saturation charge is reached. If this status is reached gases and vapors are able to move through the filter. In particular when filtering air containing toxic gases or vapors it is necessary to indicate in time before reaching the saturation that the filter is being exhausted.
Two groups of methods are known for determining the charging condition of a charcoal filter. The first group requires disassembly of or manipulation at the filter inlet and outlet. This group includes the weighting of the filter and the so called CO.sub.2 pulse test (see NRL report 6793 "The CO.sub.2 Pulse Technique for Determining Residual Gas Life of Charcoals Beds"). These methods cannot be performed when the filter is in use and don't provide a real time determination of the actual saturation condition of the filter.
A second group of methods permits the determination of the saturation level under conditions like in actual use or during simulation. In accordance with these methods gas detectors or gas indicators are provided in the filter. They provide an indication when a predetermined gas because of a reduced filtering capability of the filter can move to the location of the detector A disadvantage of these methods that these detectors or indicators respond only to particular gases or vapors. If instead of these vapors another gas or vapor is present in the air flow, an exhaust of the filter will not be recognized. Because of the combined adsorptive and chemical adsorptive effect impregnated charcoal filters provide protection against all gas like or vapor like toxic materials in air. The detectors and indicators mentioned before, however, only have a limited detection band width.
It has been proposed to embed into the charcoal filter, detectors made of SnO.sub.2 or ZrO.sub.2. These detectors permit the indication of burnable gases and accordingly can indicate the flow of carbon monoxide or methane. They are not suitable, however, to determine in ABC protective filters the passing through of nerve toxin, blood toxin or pulmonary toxin. The same limitation is valid for color indicators which are provided within the filter behind a window. With these indicators the chemical reaction of a reactive with the gas or vapor which has to be determined is indicated by means of a change of color. This change of color must be determined by looking onto the indicator. An automation of the method is possible in principle however requires a relatively complicated apparatus.
It is the object of the invention to automatically indicate the saturation level or the increase above a predetermined saturation level within a charcoal filter. The indication should be continuously present during the normal operation of the filter or during operation pauses. The method should determine and indicate the charging condition independently from the type of the adsorptively or chemisorptively bound gases or vapors. In addition sometimes it is desired to separate in the indication the water vapor content of the filter charge from the charge portion of other gases or vapors.